Evaluation of the antimicrobial property and flexural strength of the acrylic resin used in ‎orthodontic appliances containing ZnO and TiO2 nanoparticles encapsulated in zeolite

Abstract

Background: Self-curing acrylic resins, mainly composed of polymethylmethacrylate (PMMA), are widely used to manufacture removable orthodontic appliances. Self-curing acrylic resins have higher porosity than heat-curing acrylic resins leading to a susceptible place for microbial plaque colonization. Due to some of these microorganisms' activities, a very unpleasant odor is emitted from orthodontic base plates, which has adverse effects on patients' cooperation. This study aimed to investigate the antimicrobial properties of cold-curing PMMA acrylic resin containing ZnO and TiO2 nanoparticles supported in 4A zeolite and evaluating its mechanical properties. Methods: The synthesized nanoparticles were added to SR Triplex® Cold orthodontic self-curing acrylic resin powder with 2wt% and 4wt% concentrations. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy(FE-SEM), energy dispersive X-ray (EDX), MAP analysis, and Dynamic light scattering (DLS) were performed to investigate the sample's characteristics. Direct test method was used to assess the antibacterial properties of the fabricated acrylic samples against three bacterial strains Streptococcus mutans, Klebsiella Pnemoniae, and Esherichia coli. Flexural strength was evaluated by a three-point bending test, and One-way ANOVA and Tukey's post hoc test were used for statistical evaluation of data. The p-value of less than 0.05 was considered significant. Results: The addition of ZnO and TiO2 nanoparticles supported in 4A zeolite in 2wt% concentrations lead to more than 99% destruction of colonies in all three types of microorganisms. Moreover, the addition of ZnO and TiO2 nanoparticles supported in 4A zeolite in 4wt% concentrations lead to 100% destruction of colonies in all three types of microorganisms. The mean flexural strength of acrylic specimens containing 2% and 4% of synthesized nanoparticles was significantly lower than the control group. The highest amount between test groups contributed to ZnO/TiO2 supported in 4A zeolite. Despite the considerable reduction, all mean values are greater than 50 MPa. Conclusion: The addition of ZnO and TiO2 nanoparticles supported in 4A zeolite due to its potent antibacterial properties and minimal toxicity can reduce the unfavorable odor of orthodontic base plates consequently increases patient cooperation and reaching the desired result.